Windows Desktop Search is an excellent tool allowing you to have only a handful of folders outside the inbox for storing emails you may (will) need to reference in the future. You can also search across archive folders which the integrated outlook search won't let you do. I tried Google Desktop Search, and while the cache is handy if you have truly deleted something, you have to (or had to) reindex and blow away the cache to force it to reindex and find something in the archives. Copernic Desktop is also solid; I give the Windows Desktop Search the edge b/c you can drag and drop from the search results to an outlook message (or task, calendar item, etc.), so if you are looking for the email to graciously attach just to reminder the recipient that, yes, you did agree to it two months ago, you don't have to hunt it down in the folder it is stored in.